1. Technical Field
The technical field relates to an eyepiece lens system of an electronic viewfinder (EVF) which is a display apparatus that is mounted on imaging apparatuses such as television cameras, video cameras, and digital cameras and that is used to focus on a subject upon shooting or to observe the subject to determine a composition, a finder optical system including the eyepiece lens system, an electronic viewfinder including the finder optical system, and an imaging apparatus including the electronic viewfinder.
2. Related Art
An electronic viewfinder includes an LCD (liquid crystal display) and a finder optical system. The LCD displays, in the finder, a subject image on a liquid crystal display surface according to an image signal from an imaging device in an imaging apparatus. The LCD displaying the image display requires an illumination optical system that illuminates the LCD. In recent years, to meet a demand for saving space in mounting an illumination optical system, a reflective LCD has begun to be used more frequently than a transmissive LCD. In the reflective LCD, illumination light is applied thereto from the front of a liquid crystal display surface thereof. For conventional art of the reflective LCD, there is JP-A-2002-48985 that discloses a finder optical system including an eyepiece lens in which a first lens having a positive refractive index, a second lens having a negative refractive index, and a third lens having a positive refractive index are arranged on an optical axis between the liquid crystal display surface side and an observer's eye position and from the liquid crystal display surface side to the observer's eye position side. According to the description in JP-A-2002-48985, this finder optical system has a high finder magnification and is compact and can favorably correct various aberrations at low cost. As another conventional example of the finder optical system, JP-A-6-258582, for example, also discloses a finder optical system including an eyepiece lens in which first to third lenses similar to those described above are disposed. According to the description in JP-A-6-258582, a finder optical system including an eyepiece lens with excellent aberration correction, particularly, with small distortion, can be obtained.
However, while in recent years there has been a more demand for ultra-compact, high-definition reflective LCDs, market orientation is high that demands a subject image displayed on the liquid crystal display surface to be large and natural, i.e., the entire image is displayed at high resolution with no distortion, with the high-definition display being ensured. Thus, none of the techniques described in JP-A-2002-48985 and JP-A-6-258582 meet such a demand. For example, in a finder optical system described in JP-A-2002-48985, when a reflective LCD in which one pixel is about 12 μm×12 μm is used for observation, taking a look at axial chromatic aberration, even if observation is performed in sharp focus with the line e (546.1 nm) which is green, for example, 435.8 nm which is visible blue light having the shortest wavelength comes into focus at a point about 120 μm before the lens and 656.3 nm which is visible red light having the longest wavelength comes into focus at a point about 70 μm behind the lens. Thus, RGB colors that are normally mixed in one dot are separated and even when green stays within one dot and thus appears not blurred, blue and red appear blurred, which causes a problem in terms of high-definition observation. In addition, in the eyepiece lens system described in JP-A-6-258582, a magnification of only 4× is available and thus there is a problem in terms of large-scale observation with an ultra-compact LCD. Hence, in the finder optical systems proposed in the conventional documents, there is room for further improvement in terms of high definition and large-scale observation.